1. Field of the Invention
The present invention relates to an improvement of method of treating a semiconductor substrate.
More particularly, the present invention concerns an improvement of method of removing gallium residues or stains remaining on a semiconductor substrate having epitaxial growth layers of III-V compound semiconductors formed by using gallium as a solvent.
2. Prior Art
In forming epitaxial growth layer of gallium arsenide (GaAs), gallium phosphide (GaP) or gallium aluminum arsenide (GaAlAs) on a compound semiconductor substrate, a liquid phase epitaxial growth method using gallium as a solvent is being widely used. Therefore, the liquid phase epitaxial growth method is an indispensable process in manufacturing semiconductor lasers or light emitting diodes. The substrate 1, as shown in FIG. 1 necessarily have residues 2 of small lump of gallium, which are residues of the gallium as the solvent. After the epitaxial growth process, the residue stains 2 of gallium are, large or small, formed on the substrate.
Such small residue stains of the gallium are, not only no more necessary after completion of the epitaxial growth process, but also harmful for the process thereafter. Hitherto, generally, such residue stains of gallium on the substrate have been wiped off by a small ball of surgical cotton soaked with a hot water. However, such wiping off or mechanical removing is liable to form scratches or breaking of the substrate, and use of such semiconductor substrates in manufacturing semiconductor device necessarily makes devices of poor performance characteristics or of no use. When such residue stains of gallium are of a large lump, they will be easily wiped away. However, when the residue stains are very fine, a complete wiping of them will be difficult. Such residue stains of gallium will react with the electrode metal, and hence will deteriorate accuracy of the etching of the electrode metal.
A proposal of a chemical removing of the stains of the gallium retained after the mechanical wipe away, therein the removing being made by immersing the substrate into a heated chloric acid (HCl), has been already proposed. However, because the chloric acid has a nature to etch the III--V compounds, the epitaxial growth layers have been undesirably etched, and the surfaces thereof have become rough.
Thus, hitherto, no method of selectively removing the gallium residues or stains from the surface of the semiconductor substrate has been known.